C0549 code meaning
Vacuum Sensor A Circuit/Open
What C0549 means
General circuit fault of vacuum sensor A, usually a broken or disconnected signal, ground or feed line. The sensor measures the vacuum in the brake booster; Bosch notes that its value lets the system run the electric vacuum pump, permits engine stop-start and supports ESP functions. Mitsubishi shows how a brake unit watches it on the 2023 Outlander PHEV: with power on and normal supply, an open or a short in the brake vacuum sensor circuit, or signal noise, is detected within a second and stored as C1073, after which brake assist is suspended; Mitsubishi does not map that fault to an SAE code. Which physical sensor is called A is manufacturer-specific, and no maker documents C0549 publicly. C054A to C054C cover plausibility, low and high signal.
C0549 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyEasy, DIY possible
- Typical labor0.2 to 1.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of C0549
- Brake assist warning or ABS lamp on
- Stop-start no longer switching off the engine
Common causes of C0549
- Most likelySensor plug loose or not latched after work in the engine bay
- PossibleBroken signal, ground or supply wire
- Less likelyInternal open in the vacuum sensor
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Vacuum sensor aSensor wiring
What each part of C0549 means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 49 | The exact fault in that area. |
What to do next
- Note C0549 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about C0549
What does C0549 mean?
C0549 means "Vacuum Sensor A Circuit/Open". General circuit fault of vacuum sensor A, usually a broken or disconnected signal, ground or feed line. It is a generic code, so it means the same on every make.
Is it safe to drive with C0549?
Drive gently and only to a workshop. With C0549 the car can go into limp mode (reduced power) to protect itself.
Will C0549 fail an emissions test?
C0549 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is C0549 to fix?
Difficulty: easy. A typical repair takes 0.2 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will C0549 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.